Blue lights used by CSIs (Crime Scene Investigators or Scenes of Crime Officers) help detect fingerprints and other evidence by creating contrast. Think of standing on one side of a large field and looking across the field at someone standing among some trees. Imagine that maybe they are smoking a cigarette. If it is daytime, you might have a really tough time spotting a cigarette or other evidence they are smoking unless you are using binoculars or a telescope (which is the equivalent of a forensic scientist in a crime lab using a microscope to look for evidence).

Next, imagine that it is night time and you are looking across the field at someone standing among trees smoking a cigarette. It is often pretty easy to spot the bright glow of a cigarette when they take a puff... or the bright flame of a cigarette lighter or matches when they light a cigarette. The reason the glowing is easy to spot is not because it glows more during the night, but because there is more contrast between the glowing and the dark area surrounding the cigarette or lit match/lighter.

When you see CSI folks using blue lights, green lights, UV light, portable lasers, and alternate light sources, they are trying to make evidence glow so it is easier to spot. To do so with blue lights, they normally use a filter (orange, red, etc.) to block much of the blue or green light but permit the glowing light to pass through. A more detailed explanation of glowing (technically called photoluminescence) can be found here.

Cassidy Colson

Posted on Tuesday, November 29, 2005 - 02:05 pm:

Heys,

My name is cassidy colson I am working on a project about fingerprints I -NEED- to know all the info I can learn on fingerprints. Well back to my question how does the blue lights and things like that help CSIs detect fingerprints

If anyone can help me find a website or just to answer my question

Thanks

bye Cassidy Colson

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